Coupled spin models for magnetic variation of planets and stars

TL;DR

This paper develops a minimal coupled spin model to explain magnetic variations in planets and stars, capturing key features like polarity reversals, power spectra, and cyclic behavior, and provides scaling relations consistent with observations.

Contribution

It introduces a simplified coupled macro-spin model that reproduces observed geomagnetic and stellar magnetic features, including polarity flips and cycles.

Findings

Model reproduces geomagnetic polarity reversals and fluctuations.

The model explains solar magnetic cycle quasi-regularity.

Scaling relations match observations across celestial bodies.

Abstract

Geomagnetism is characterized by intermittent polarity reversals and rapid fluctuations. We have recently proposed a coupled macro-spin model to describe these dynamics based on the idea that the whole dynamo mechanism is described by the coherent interactions of many small dynamo elements. In this paper, we further develop this idea and construct a minimal model for magnetic variations. This simple model naturally yields many of the observed features of geomagnetism: its time evolution, the power spectrum, the frequency distribution of stable polarity periods, etc. This model has coexistent two phases; i.e. the cluster phase which determines the global dipole magnetic moment and the expanded phase which gives random perpetual perturbations that yield intermittent polarity flip of the dipole moment. This model can also describe the synchronization of the spin oscillation. This corresponds to the case of sun and the model well describes the quasi-regular cycles of the solar magnetism. Furthermore, by analyzing the relevant terms of MHD equation based on our model, we have obtained a scaling relation for the magnetism for planets, satellites, sun, and stars. Comparing it with various observations, we can estimate the scale of the macro-spins.